Here's why:
* Phylum: A major grouping of animals based on shared fundamental characteristics.
* Chordata: This phylum includes all animals with a notochord (a flexible rod that supports the body), a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail at some stage of development.
* Mammals: A class within Chordata that possess specific characteristics like mammary glands, hair, warm-bloodedness, and a more complex nervous system.
So, mammals belong to the larger group of Chordates, alongside other animals like fish, amphibians, reptiles, and birds.